VYPR
← All advisories
High severityNVD Advisory· Published Mar 16, 2026· Updated Mar 16, 2026

Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle

CVE-2026-28490

Description

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a cryptographic padding oracle vulnerability was identified in the Authlib Python library concerning the implementation of the JSON Web Encryption (JWE) RSA1_5 key management algorithm. Authlib registers RSA1_5 in its default algorithm registry without requiring explicit opt-in, and actively destroys the constant-time Bleichenbacher mitigation that the underlying cryptography library implements correctly. This issue has been patched in version 1.6.9.

Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
authlibPyPI
< 1.6.91.6.9

Affected products

1

Patches

1
48b345f29f6c

fix(jose): remove deprecated algorithm from default registry

https://github.com/authlib/authlibHsiaoming YangFeb 25, 2026via ghsa
commit
6 files changed · +21 −5
  • authlib/jose/rfc7515/jws.py+6 −2 modified
    @@ -261,12 +261,16 @@ def _prepare_algorithm_key(self, header, payload, key):
             raise MissingAlgorithmError()
 
         alg = header["alg"]
-        if self._algorithms is not None and alg not in self._algorithms:
-            raise UnsupportedAlgorithmError()
         if alg not in self.ALGORITHMS_REGISTRY:
             raise UnsupportedAlgorithmError()
 
         algorithm = self.ALGORITHMS_REGISTRY[alg]
+        if self._algorithms is None:
+            if algorithm.deprecated:
+                raise UnsupportedAlgorithmError()
+        elif alg not in self._algorithms:
+            raise UnsupportedAlgorithmError()
+
         if callable(key):
             key = key(header, payload)
         key = algorithm.prepare_key(key)
  • authlib/jose/rfc7515/models.py+1 −0 modified
    @@ -5,6 +5,7 @@ class JWSAlgorithm:
 
     name = None
     description = None
+    deprecated = False
     algorithm_type = "JWS"
     algorithm_location = "alg"
  • authlib/jose/rfc7516/jwe.py+11 −3 modified
    @@ -697,11 +697,19 @@ def get_header_alg(self, header):
             raise MissingAlgorithmError()
 
         alg = header["alg"]
-        if self._algorithms is not None and alg not in self._algorithms:
-            raise UnsupportedAlgorithmError()
         if alg not in self.ALG_REGISTRY:
             raise UnsupportedAlgorithmError()
-        return self.ALG_REGISTRY[alg]
+
+        instance = self.ALG_REGISTRY[alg]
+
+        # use all ALG_REGISTRY algorithms
+        if self._algorithms is None:
+            # do not use deprecated algorithms
+            if instance.deprecated:
+                raise UnsupportedAlgorithmError()
+        elif alg not in self._algorithms:
+            raise UnsupportedAlgorithmError()
+        return instance
 
     def get_header_enc(self, header):
         if "enc" not in header:
  • authlib/jose/rfc7516/models.py+1 −0 modified
    @@ -9,6 +9,7 @@ class JWEAlgorithmBase(metaclass=ABCMeta):  # noqa: B024
 
     name = None
     description = None
+    deprecated = False
     algorithm_type = "JWE"
     algorithm_location = "alg"
  • authlib/jose/rfc7518/jwe_algs.py+1 −0 modified
    @@ -52,6 +52,7 @@ class RSAAlgorithm(JWEAlgorithm):
 
     def __init__(self, name, description, pad_fn):
         self.name = name
+        self.deprecated = name == "RSA1_5"
         self.description = description
         self.padding = pad_fn
  • authlib/jose/rfc7518/jws_algs.py+1 −0 modified
    @@ -27,6 +27,7 @@
 class NoneAlgorithm(JWSAlgorithm):
     name = "none"
     description = "No digital signature or MAC performed"
+    deprecated = True
 
     def prepare_key(self, raw_data):
         return None

Vulnerability mechanics

Generated by null/stub on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.

References

5

News mentions

0

No linked articles in our index yet.